Liquid crystalline medium and liquid crystal display

Details Liquid crystalline medium and liquid crystal display Liquid crystalline medium and liquid crystal display

2002-10-23

2004-07-13

Wu, Shean C. (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C252S299610, C252S299630, C252S299660

Reexamination Certificate

active

06761939

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to liquid crystalline media and to liquid crystal displays comprising these media, especially to displays addressed by an active matrix (AMDs) and in particular to displays addressed by thin film transistors (TFTs), especially for projection type displays. Preferably, the TFTs are prepared on silicon (LCoS). The inventive media are also well suited for displays of the optically compensated bend (OCB) mode.
PROBLEM TO BE SOLVED AND STATE OF THE ART
Liquid Crystal Displays (LCDs) are widely used to display information. Electro-optical modes employed are, e.g., the twisted nematic (TN)-, the super twisted nematic (STN)-, the optically compensated bend (OCB)- and the electrically controlled birefringence (ECB)-mode with their various modifications, as well as others. Besides these modes, which all do use an electrical field, which is substantially perpendicular to the substrates, respectively to the liquid crystal layer, there are also electro-optical modes employing an electrical field substantially parallel to the substrates, respectively the liquid crystal layer, like, e.g., the In-Plane Switching mode (as disclosed, e.g., in DE 40 00 451 and EP 0 588 568). Especially this electrooptical mode is used for LCDs for modern desk top monitors.
The liquid crystals according to the present invention are preferably used in AM addressed displays in particular in TFTs displays, especially for projection type displays. Preferably the TFTs are prepared on silicon (LCoS). The inventive media are also well suited for displays of the OCB mode.
For these displays new liquid crystalline media with improved properties are required. Especially the birefingence (&Dgr;n) should be sufficiently high. Further, the dielectric anisotropy (&Dgr;&egr;) should be high enough to allow a reasonably low operation voltage. Preferably, &Dgr;&egr; should be higher than 7 and very preferably be higher than 9, or even higher than 10, but preferably not higher than 19 and in particular not higher than 15. Otherwise, the resistivity of the mixtures tends to become inacceptably low for most TN-AMDs. Besides this parameter, the media have to exhibit a suitably wide range of the nematic phase, a rather small rotational viscosity and, as mentioned above, an at least moderately high specific resistivity.
The displays according to the present invention are preferably addressed by an active matrix (active matrix LCDs, short AMDs), preferably by a matrix of thin film transistors (TFTs). However, the inventive liquid crystals can also beneficiously be used in displays with other known addressing means.
There are various different display modes using composite systems of liquid crystal materials of low molecular weight together with polymeric materials such as, e.g., polymer dispersed liquid crystal (PDLC)-, nematic curvilinearily aligned phase (NCAP)- and polymer network (PN)-systems, as disclosed, for example, in WO 91/05 029 or axially symmetric microdomain (ASM) systems and others. In contrast to these, the modes especially preferred according to the instant invention are using the liquid crystal medium as such, oriented on surfaces. These surfaces typically are pretreated to achieve uniform alignment of the liquid crystal material. The display modes according to the instant invention preferably use an electrical field substantially perpendicular to the composite layer.
LCDs are used for direct view displays, as well as for projection type displays.
Liquid crystal compositions with a high value of the birefringence suitable for LCDs and especially for AMD displays are known, e.g., from U.S. Pat. No. 5,328,644, JP 06-264 059 (A) and DE 199 19 348. These compositions, however, do all have significant drawbacks. Most of them have, amongst other deficiencies, too low values of the birefringence and/or require operation voltages which are too high. Many of them also have too low resistivities, especially after exposure to elevated temperature and/or intense actinic radiation, in particular strong visible light and/or UV radiation. Many of the media of the prior art do further lead to unfavourably long response times.
Thus, there is a significant need for liquid crystalline media with suitable properties for practical applications such as a wide nematic phase range, low viscosities, a high &Dgr;&egr;, a sufficiently high resistivity and, in particular, an appropriately high optical anisotropy &Dgr;n, according to the display mode used.
PRESENT INVENTION
Surprisingly, it now has been found that liquid crystalline media with a suitably high &Dgr;&egr;, a suitable phase range, &Dgr;n and a sufficiently high resistivity can be realised, which do not exhibit the drawbacks of the materials of the prior art or at least do exhibit them to a significantly lesser degree.
These improved liquid crystalline media according to the instant application comprise at least the following components:
a dielectrically positive component, component A, consisting of dielectrically positive compounds, comprising one or more compounds of formula I, one or more compounds of formula II and optionally one or more compounds, preferably selected from the group of compounds of formulae of formula III, IVa and V and optionally further dielectrically positive compounds
wherein
R
1
, R
2
, R
3
, R
4
and R
5
independently of each other, are alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy with 1 to 7 C-atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl with 2 to 7 C-atoms,
X
1
, X
2
, X
3
and X
5
independently of each other, are F, Cl or fluorinated alkyl or fluorinated alkoxy, each with 1 to 4 C-atoms, preferably
X
1
and X
5
are, independently of each other, F or Cl, most preferably F and
X
2
and X
3
are, independently of each other, F or Cl, most preferably Cl,
X
4
is fluorinated alkyl or fluorinated alkoxy, each with 1 to 4 C-atoms, preferably OCF
3
or OCF
2
H,
Y
51
and Y
52
are, independently of each other, H or F and
n is 0, 1 or 2, preferably 1 or 2, most preferably 2,
wherein, optionally, two of the 6-membered rings in formulae I, and III to V may be linked by a group selected from
—CH
2
—CH
2
—, —CF
2
—CF
2
—, —CF
2
—O—, —O—CF
2
— and —CO—O—, preferably —CH
2
—CH
2
— and —CF
2
—O—, most preferably —CH
2
—CH
2
—,
a dielectrically neutral component, component B, consisting of dielectrically neutral compounds, comprising one or more compounds of formula IVb
wherein
R
4′
is alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy with 1 to 7 C-atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl with 2 to 7 C-atoms,
X
4′
is F or Cl, preferably F,
wherein, optionally, two of the 6-membered rings may be linked by a group selected from
—CH
2
—CH
2
—, —CF
2
—CF
2
—, —CF
2
—O—, —O—CF
2
— and —CO—O—, preferably —CH
2
—CH
2
— and —CF
2
—O—, most preferably —CH
2
—CH
2
—, and
optionally, a dielectrically negative component, component C, consisting of dielectrically negative compounds.
Preferably, the dielectrically positive component, component A comprises one or more compounds each of formulae I, II IVb and one or more compounds selected from the group of compounds each of formulae III, IVa and V and in particular one or more compounds each of formulae III and V.
Further, the dielectrically positive component, component A, optionally comprises one or more compounds of formula VI
wherein
R
6
is alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy with 1 to 7 C-atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl with 2 to 7 C-atoms,
X
6
is F, Cl or fluorinated alkyl or fluorinated alkoxy, each with 1 to 4 C-atoms, preferably F or Cl, most preferably F,
Y
6
is H or F and
m is 0, 1 or 2, preferably 1 or 2 and most preferably 1,
wherein, optionally, two of the 6-membered rings may be linked by an group selected from
—CH
2
—CH
2
—, —CF
2
—CF
2
—, —CF
2
—O—, —O—CF
2
— and —CO—O—, preferably —CH
2
—CH
2
— and —CF
2
—O—, most preferably —CH
2
—CH
2
—
The liqiud crystral mixtures according to the present invention comprise a dielectrically neutral comp

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